Field
Embodiments of the present invention generally relate to elastically deformable items of sports equipment or pieces of play equipment, such as inflatable balls, and more particularly to elastically deformable items of sports equipment comprising at least one deformable electromagnetic coil structure arranged around a curved surface within the item of sports equipment.
Description of Conventional Art
An electromagnetic coil, or simply a coil, is formed when an electrical conductor, such as a copper wire, is wound to generate an inductive or electromagnetic element. Here, the wire may also be wound around a core or a form. One loop of wire may be referred to as a turn, and a coil comprises one or more turns. Coils serving as inductors and/or inductances are widespread in electronic circuits as a passive two-terminal electrical component that stores energy in its magnetic field. For example, coils may be used for realizing transformers by means of which energy is transferred from one electrical circuit to another by inductive coupling without moving parts. Furthermore, coils may be used to build resonant circuits comprising serial and/or parallel arrangements of inductors and capacitors. In some applications, coils may also serve as antennas or antenna-like elements for detecting electromagnetic fields, such as in Radio Frequency Identification (RFID) or similar applications.
In one of such applications, for example, it is proposed to detect the transition of a moving playing object, such as a ball or a puck, through a detection plane (e.g., a goal plane) using electromagnetic fields and/or signals. In some types of ball sports, e.g., soccer or football, the use of automated goal-detection systems is discussed in order to avoid human errors in decision-making. In this context, the so-called goal-line technology is a technology which can determine when the ball has crossed the goal line, assisting the referee in awarding a goal or not. There are various alternative approaches for determining the exact position or location of the ball, such as video-based or electromagnetic field-based systems. In an electromagnetic field-based system, a moving object, such as a ball, may be equipped with an electronic circuit for transmitting and/or receiving and/or reflecting electromagnetic signals. For such electromagnetic approaches, electronic components are required inside the ball, wherein the size of the electronics may differ depending on its functionality and the used frequency range. For small and medium-sized systems, electronics may be installed within the center of the ball, for example. For goal-detection systems requiring more area and volume, e.g., for systems using magnetic fields in the sub-MHz range, the required loop antennas and/or the further electronic components may be installed on the circumference of the ball.
In order to achieve detection properties which are as rotationally invariant as possible, one goal-detection system proposes to install three orthogonally arranged coils or loop antennas within or on a moving object, e.g., a ball, to emit or reflect at least a part of an electromagnetic field. Due to this orthogonal arrangement of the coils, the rotational position of the ball has only little influence on the electromagnetic emission or reflection properties, as, in theory, the three orthogonal loop antennas result in an effective loop antenna, whose effective opening surface is perpendicular to an incident magnetic field coming from a transmitter installed at or near the goal. That is to say, the normal of the effective opening surface of the effective loop antenna is essentially parallel to the magnetic field vector.
For a correct functioning, i.e., high precision of goal-detection systems, the electromagnetic properties of the ball or a puck are of crucial importance. In one exemplary goal-detection system, a magnetic field may be generated by means of a current-carrying conductor extending around a goal frame. The generated magnetic field is here perpendicular to a detection plane defined by the goal frame. This stimulating magnetic field is reflected by the ball, wherein the reflected signal should generate the same directional vector as the stimulating field (due to the ball electronics with a phase shift). The geometric accuracy of the reflected signal directly influences the measurement result and, hence, the accuracy of the goal decision.
The detection system is based on three orthogonal coils in the ball. Each of the coils may comprise a plurality of turns which may, for example, be inserted between the ball bladder and the outer ball skin or the cover material of the ball. In order to obtain an adequate quality of a resonant coil in the ball, the diameter of the coil(s) should be as large as possible, which means that the coil(s) should be installed in or underneath the ball cover material.
However, as a result of the elasticity of the ball cover material which, for example, may consist of several leather patches, all pulses which strike the ball from the outside may be directly passed on to a coil in the ball. For the coil not to break as a result of such pulses, the coil itself should be elastic. It is known to insert coils with electrical conductors in a meandering manner into a ball, such that a longitudinal axis of the coil(s) can be elongated in circumferential direction, respectively. However, on account of the permanent load on the coil, fatigue fractures already occur at the corners of the meandering conductor before the end of the required operating life. Exemplary breaking points which are to be attributed to fatigue fractures of a coil structure are schematically illustrated in FIG. 1.
Hence, there is a demand for providing an improved concept for arranging one or several coil(s) into balls or items of sports equipment in general.